Heat exchangers already known for use in industrial machines such as oil cooler, aftercoolers and radiators include those comprising fluid passing hollow portions of aluminum extending laterally and arranged one above another in parallel at a spacing, aluminum spacers arranged between each pair of adjacent fluid passing portions at the left and right ends thereof and brazed to the fluid passing portions, and a corrugated aluminum fin provided between and brazed to each pair of adjacent fluid passing portions and positioned between the left and right spacers, each of the fluid passing portions comprising a flat hollow body having an upper and a lower flat wall and a peripheral wall interconnecting the upper and lower walls along peripheral edges thereof, each of the upper and lower walls of the flat hollow body having a hole formed in each of left and right end portions thereof, each of the left and right spacers having a through hole communicating with the corresponding holes in the upper and lower walls of the flat hollow body, a pair of left and right headers extending vertically and each provided by all the spacers at each of the left and right ends of the heat exchanger and the portions of the hollow flat bodies positioned between the spacers at the exchanger end (see the publications of JP-A No. 2001-82891 and JP-A No. 1996-233476).
The flat hollow body comprises two flat plates arranged one above the other at a spacing and each made of an aluminum brazing sheet having a brazing material layer over opposite surfaces thereof, and a channel forming body of aluminum disposed between and brazed to the flat plates, each of the flat plates having a hole formed in each of left and right opposite end portions thereof, the channel forming body comprising a peripheral wall interconnecting the peripheral edges of the two flat plates and a heat transfer area increasing portion interconnecting lengthwise intermediate parts of two straight portions of the peripheral wall which are positioned respectively along the front and rear opposite side edges of the flat plates. The two flat plates serve as the upper and lower walls of the flat hollow body, and the peripheral wall of the channel forming body serves as the peripheral wall of the flat hollow body.
However, the conventional heat exchanger has the following problems. Since each pair of adjacent flat hollow bodies have spacers therebetween respectively at the left and right opposite ends thereof, the exchanger has relatively great weight in its entirety. Stated more specifically, the spacer needs to be provided with a through hole for passing therethrough a high-temperature fluid having a high pressure, so that the spacer peripheral wall defining the hole must have an increased thickness, consequently increasing the weight of the spacer and therefore the weight of the overall heat exchanger.
Since the through hole is formed in each spacer, it is impossible to form screw holes in the spacer for use in attaching a bracket or boss to the spacer. The bracket or boss accordingly needs to be fixed in position by welding through a cumbersome procedure. Although the spacer peripheral wall defining the through hole must be given an increased thickness if screw holes are to be formed in the spacer for use in attaching the bracket or boss thereto, this results in a further increase in the weight of the entire heat exchanger.
Because the heat exchanger has the headers at the respective left and right ends thereof, the area of the unit wherein the high-temperature fluid and the low-temperature fluid are subjected to heat exchange, namely, the area of the core unit, is small relative to the overall size of the heat exchanger required for the installation of the exchanger. This imposes limitations on the effect to improve the heat exchange efficiency.
The high-temperature fluid flows into one of the headers and thereafter flows through the flat hollow bodies into the other header. In the meantime, the high-temperature fluid is subjected to heat exchange with the low-temperature fluid flowing forward from the rear between the pairs of adjacent hollow bodes. In this case, the portion of high-temperature fluid flowing in the rear side portions of the hollow bodies is efficiently cooled with the low-temperature fluid, whereas the low-temperature fluid reaching the front side portions of the hollow bodies is already given a relatively high temperature and therefore less efficiently cools the high-temperature fluid flowing through the front side portions of the hollow bodies. Consequently, the heat exchanger is not fully satisfactory in overall heat exchange efficiency.
An object of the present invention is to overcome the above problems and to provide a fluid passing flat hollow body which is usable for a heat exchanger which is smaller in weight and higher in heat exchange efficiency than the conventional heat exchanger, a heat exchanger comprising such fluid passing flat hollow bodies, and a process for fabricating the heat exchanger.